Led by the example of Bernard of Clairvaux, Cistercian monks turned their attention to the world outside the monastery walls in response to the threat posed by heretical Christians, in particular the Cathars. The white monks, with other intellectuals, turned to pen, pulpit and popular preaching to counteract heresy, some accepting posts as bishops and papal legates, helping and even directing the Albigensian crusade, and contributing to the formulation...